1. Field of the Invention
This invention relates to a rotor of a superconductive rotary electric machine, and more particularly to the mounting structure of the superconductive field coils on the coil-carrying shaft of such a rotor.
2. Description of the Prior Art
The electrical resistance of certain metals, such as lead, tin, and vanadium, and alloys, such as niobium-tin and niobium-titanium, become vanishingly small, i.e. they become superconductive, when the temperature thereof falls below the transition temperatures thereof which are in the neighbourhood of a few degrees above absolute zero. Thus, when the field windings of an alternating current generator, for example, are formed of such a superconductive material and cooled below the transition temperature thereof, then a large magnetic field can be established without the expenditure of appreciable amounts of electrical energy. Alternating current generators having rotors which carry superconductive field windings have already been constructed. In such superconductive rotors, however, secure and reliable mounting of the superconductive field coils on the coil-carrying shaft of the rotor is of paramount importance, because when the field coils are displaced by the vibrations due to the rotational movement of the rotor, the resulting frictional heat may destroy the superconductivity of the field coils. Further, as the field coils much be covered many times by a complicated covering structure for the purpose of preventing outside heat from entering thereinto, the checking and repairing thereof are difficult to perform.
Thus, it has already been proposed to wind the superconductive field coils around bobbins and then to mount the bobbins on the outer surface of the coil-carrying shaft. This makes it possible to wind the field coils separately from the coil-carrying shaft at a place where the winding operation can be performed effectively and reliably. The bobbins, however, make the dimension of the rotor larger and increase the production cost and production time thereof.
Thus, another mounting structure for mounting the field coils on the coil-carrying shaft has been proposed to solve the above-mentioned problem caused by using bobbins. Namely, grooves having forms corresponding to the rectangular-loop-shaped field coils are formed on the outer surface of the coil-carrying shaft, and the field coils are accommodated in these grooves. A plurality of wedges are then fitted into recesses formed in the side surfaces of the grooves above the portions thereof which accommodate the field coils, thereby keeping the field coils situated thereunder securely in the proper positions thereof. The portions of the grooves running in the circumferential direction of the coil-carrying shaft, however, have the form of circular arcs and wedges of this shape for use according to this method are difficult to machine. The wedges and the recesses corresponding to these circumferentially running portions of the grooves are also curved. The complicated forms of the circumferentially running portions of the grooves and wedges result not only in increased production time and cost, but also in difficulty in the precise and reliable machining thereof.